The invention relates to a movable wiper or slider for potentiometers, variable resistances or the like, as well as for the transmission of current from rotating parts, the former consisting of at least one elastic finger, which rests under pressure on a current-conducting path (runway).
In a multitude of electrical instruments, components and systems, movable wipers or sliders are required and used, which tap, for example, variable voltage potentials from a suitable, exposed resistance. In the following, the invention and facts connected with the latter are discussed in greater detail by means of a potentiometer, and specifically, a circular potentiometer. In such a potentiometer, the path of resistance or runway is applied in form of a coat of material onto a carrier material and scanned by a movable wiper sliding over the path of resistance. Such potentiometers are of considerable importance in the various areas of technology, particularly in process control, the generation of saw-tooth voltages, as a so-called sine-cosine potentiometer, and the like. In fact, such potentiometers can be designed so as to be the only mechanically moving switching elements in entire control systems, whereby it depends on the possible speed, with which the slider or wiper can yet be moved over the runway, i.e. the path of resistance, whether the most varied control and guide tasks can be carried out in an unobjectionable manner.
As well known to the experts of the art, considerable problems arise in the practical manufacture and use of such potentiometers, which are in the main attributable to the fact that the slider or wiper is subjected to vibrations during its sliding motion over the path of the resistance material. These vibrations are caused due to the fact that the slider is forced to rest under a certain pressure on the runway formed by the path of resistance, while this runway, although presenting a completely smooth appearance to the human eye, exhibits on the other hand a considerable unevenness which, when observed with great magnification, shows an array of irregularly arranged mountains, valleys, cavities, humps, grooves, and the like. A slider guided over such a path of resistance is in principle in constant vertical motion caused by this formation of mountains and valleys, and it is only a question of the working velocity, i.e. the relative speed between runway and slider, when appropriate resonant ranges are attained which will cause the slider (and possibly the runway) to be destroyed in a matter of minutes. In the course of such destruction, the individual slider fingers will break off; that is they are literally torn apart and the surfaces of slider and runway, which grind against each other, are rapidly destroyed to an extent that the whole potentiometer becomes quickly unusable.
Of course, such problems are well-known to the experts, and many steps have already been taken to remedy this situation. It should still be pointed out that one of the first essential steps is that of dividing the slider or at least the slider area gliding along the runway into a plurality of individual fingers, e.g. five or more, which represent by themselves each an elastic system and are capable of moving independently from the others. Such sliders can be produced by stamping the fingers out of a suitable sheet metal or by combining a large number of wire-like fingers in a parallel arrangement. At those points where the individual slider fingers rest on the runway, they are bent upward again, thus causing the slider finger to glide along the runway with a definite external radius.
As a first possibility, an attempt has been made to finish the runway, which consists of a suitable resistance material, for instance a carbon coating, in such a way that the roughness of the runway is largely eliminated, i.e. the runway may be honed or polished with a high degree of precision. It seems logical, however, that this process will result merely in a shifting of the problems, for instance into higher speed ranges of the relative movement between slider and runway, for in this case too, vibrations cannot be eliminated. Furthermore, the slider fingers themselves will act as elements of destruction on the runway after a certain period, causing the irregularities in the runway to reappear. In addition, the sliders frequently cannot be prevented from moving in preferred positions at the expense of others, which results in an uneven use of the runway in a longitudinal direction, causing the old problems to reappear after a short period with extremely rapid rotational motion, even when a resistance path polished with high precision was made available at the time of manufacture.
It also has been tried previously to counter the destruction of slider fingers and of the runway by increased spring pressure or by manufacturing the individual fingers themselves from a relatively stiff material (slight elasticity), and bringing all of them to bear on an extremely elastic carrier material. This solution, as well as the additional step of fashioning the individual slider fingers variable in length, proved however unsatisfactory in the long run because the old destruction tended to recur again and again in certain rotational speed ranges. Although efforts of providing the individual fingers with variable resonant frequencies were crowned with success as a result of the aforementioned measure of producing the slider fingers in varying lengths, and this resulted initially in a relatively satisfactory readability of the scanned voltage, destruction of certain fingers at their assigned resonant frequencies could not be prevented, causing the entire potentiometer in the long run to exhibit constantly increasing failure symptoms.
The data expected from a conventional potentiometer can therefore only be approximately of the order of magnitude of 400 to 1000 revolutions/minute, with a total life span of no more than 1 to 2 million revolutions. Such data must be regarded, however, as the upper limit. Under no circumstances are they adequate, however, and they do not permit satisfactory use of potentiometers for high-speed processing of control data, the control of machinery and the like.
The difficulties and problems resulting from the employment of such potentiometers operating with high speeds in modern processing systems, control data equipment etc. are therefore of a complicated nature and of extraordinary importance. They have not been solved to this day in a satisfactory manner and the potentiometers used constituted therefore in each case the weakest link in the chain of components used.